The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The HDA includes a disk drive base that, together with a disk drive cover, enclose at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The PCBA includes electronics and firmware for controlling the rotation of the spindle motor and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The spindle motor typically includes a rotor including one or more rotor magnets and a rotating hub on which disks are mounted and clamped, and a stator. If more than one disk is mounted on the hub, the disks are typically separated by spacer rings that are mounted on the hub between the disks. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the rotor magnet(s), thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks.
The HSA typically includes a head actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. During operation of the disk drive, the head actuator must rotate to position the HGAs adjacent desired information tracks on the disk. The head actuator includes a pivot-bearing cartridge to facilitate such rotational positioning. The pivot-bearing cartridge fits into a bore in the body of the head actuator. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body, and is disposed opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, to form a voice coil motor. The PCBA provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator.
Each HGA includes a head for reading or writing data from and to the disk. In magnetic recording applications, the head typically includes a slider and a magnetic transducer that comprises a writer and a read element. In optical recording applications, the head may include a mirror and an objective lens for focusing laser light on to an adjacent disk surface. The slider is separated from the disk by a gas lubrication film that is typically referred to as an “air bearing.” The term “air bearing” is common because typically the lubricant gas is simply air.
However, air bearing sliders have been designed for use in disk drive enclosures that contain helium, because an inert gas may not degrade lubricants and protective carbon films as quickly as does oxygen. Helium may also be used, for example, because it has higher thermal conductivity than air, and therefore may improve disk drive cooling. Also, because the air bearing thickness depends on the gas viscosity and density, the air bearing thickness may be advantageously reduced in helium relative to air (all other conditions being the same). Furthermore, because helium has lower density than air, its flow (e.g. flow that is induced by disk rotation) may not buffet components within the disk drive as much, which may reduce track misregistration and thereby improve track following capability—facilitating higher data storage densities. Even where the disk drive enclosure contains only helium, or only nitrogen, or much more helium than air, the gas lubrication film between the head and the disk may still be referred to as an “air bearing” for convenience, and the surface of the head facing that film may still be referred to as an “air bearing surface” for convenience.
Disk drive enclosures disclosed in the art to contain helium are typically hermetically sealed to prevent an unacceptable rate of helium leakage. Although some negligible amount of helium leakage is unavoidable, helium leakage is undesirable because it can alter the thickness of the gas lubrication film between the head and the disk, and thereby affect the performance of the head. Helium leakage is also undesirable because it can alter the tribochemistry of the head disk interface, possibly leading to degradation in reliability, head crashes, and associated data loss.
Various methods and structures that have been disclosed in the past to hermetically seal disk drive enclosures have been too costly, have required too much change to existing disk drive manufacturing processes, and/or were not able to retain helium internal to the disk drive enclosure for sufficient time to ensure adequate product reliability. Thus, there is a need in the art for disk drive enclosure sealing methods and structures that may be practically implemented and integrated in a high volume and low cost disk drive manufacturing process, and that can reduce helium leakage rates enough to retain helium internal to a disk drive enclosure for a sufficient period of time to ensure adequate post-manufacture product reliability and lifetime.